Method for printed circuit board repair

ABSTRACT

A method and apparatus for efficiently repairing or reworking a printed circuit board having a solder ball grid array thereon efficiently and at minimum cost includes the steps of drilling out a plated-through hole to sever electrical connections between a ball grid array pad on one surface of the printed circuit board and internal circuits and circuits on an opposite surface of the printed circuit board; inserting a pin having an insulated sleeve surrounding a portion thereof into the drilled-out hole, the pin having attached to one end a wire for attachment to the ball grid array on one surface of the printed circuit board and a post at the other end of the pin for attachment of a wire to the post; the pin having a stop along its length to control vertical positioning of the pin in the drilled-out hole, the pin referred to as a via replacement (VR) pin. Alternately, after the plated through hole is drilled out, an insulated wire may be inserted into the hole with insulation removed from the length of the wire which extends beyond one surface of the printed circuit board. The bare length of wire is bent parallel to the surface of the printed circuit board and attached thereto by a solder reflow process. In a dog bone configuration, the wire is formed around a pad on the surface of the printed circuit board which receives the solder ball.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to printed circuit boards used inelectronic systems and, more particularly, to a method and apparatus forreworking or repairing printed circuit boards including solder ball gridarrays.

2. Prior Art.

An article in the IBM Technical Disclosure Bulletin (TDB), Vol. 24, No.2, July 1981, at p. 1237, shows an insulating device for plugging adrilled-out hole in a printed circuit board (PCB). The article does notteach the method or apparatus in accordance with the present inventionas taught and claimed herein.

An article in the IBM TDB, Vol. 33, No. 1B, June 1990, at p. 475,teaches a device for repairing a printed circuit net using a coaxialcable-to-board pin connection. The articles shows a method forreconstructing a deleted internal net of the PCB by utilizing aninsulated bifurcate connector pin with an extended tail which providespluggability with a coaxial cable. The article does not describe how theconnector would be connected to pads in a ball grid array, and further,the physical size of the device shown in the article is much too largefor use with a ball grid array pattern on a printed circuit board. Inany event, the article does not teach nor suggest the present inventionas taught and claimed herein.

An abstract No. 34488, published in Research Disclosure, December 1992,No. 344, by Kenneth Mason Publications, Ltd., shows a method forrepairing open circuits in a printed circuit board. However, the articledoes not teach nor suggest the present invention as taught and claimedherein.

An article in the IBM TDB, Vol. 36, No. 12, December 1993, at p. 133,teaches a technique for reworking solder ball connections, engineeringchange or wire add to a printed circuit board. Although the articleshows both via-in-pad and dog bone configurations, the article does notteach nor suggest either the wire loop technique nor the rigid pinstructure as is taught and claimed herein.

U.S. Pat. No. 3,230,297 teaches a circuit board with a connector withsolder resistant portions. However, the patent teaches a repair of asimple double-sided board rather than current multi-layer boards, andthe patent does not address the problems associated with ball gridarrays as are taught and claimed herein.

U.S. Pat. No. 3,361,869 teaches an apparatus for making connections to aprinted circuit board and for circuit line repair. However, the patentdoes not teach nor suggest the present invention as taught and claimedherein.

U.S. Pat. No. 3,406,246 teaches an apparatus for repair of printedcircuit lines on a double-sided printed circuit board. However, thepatent does not teach nor suggest the present invention as taught andclaimed herein.

U.S. Pat. No. 4,409,732 teaches a circuit isolator element for use inisolating leads while testing components on a printed circuit board.However, the patent does not teach nor suggest the present invention astaught and claimed herein.

U.S. Pat. No. 4,778,556 teaches an apparatus for correcting or repairingprinted circuit boards. The patent only teaches adding conductors to anexisting printed circuit board. The patent does not teach nor suggestdeletion of printed circuits nor ball grid array processing as aretaught and claimed herein.

Although the prior art generally discusses repairing or reworkingprinted circuit boards, the prior art does not address the problem ofisolating circuits and reconnection to a ball grid array in state of theart printed circuit board structures which have extremely small spacing.

SUMMARY OF THE INVENTION

It is an object of the present invention to rework or repair a printedcircuit board efficiently and at minimum cost.

Accordingly, method and apparatus for efficiently repairing or reworkinga printed circuit board having a solder ball grid array thereonefficiently and at minimum cost includes the steps of drilling out aplated-through hole to sever electrical connections between a ball gridarray pad on one surface of the printed circuit board and internalcircuits and circuits on an opposite surface of the printed circuitboard; inserting a pin having an insulated sleeve surrounding a portionthereof into the drilled-out hole, the pin having attached to one end awire for attachment to the ball grid array on one surface of the printedcircuit board and a post at the other end of the pin for attachment of awire to the post; the pin having a stop along its length to controlvertical positioning of the pin in the drilled-out hole, the pinreferred to as a via replacement (VR) pin.

Alternately, after the plated through hole is drilled out, an insulatedwire may be inserted into the hole with insulation removed from thelength of the wire which extends beyond one surface of the printedcircuit board. The bare length of wire is bent parallel to the surfaceof the printed circuit board and attached thereto by a solder reflowprocess. In a dog bone configuration, the wire is formed around a pad onthe surface of the printed circuit board which receives the solder ball.

It is an advantage of the present invention that a printed circuit boardmay be reworked in such a fashion so as to be compatible with connectionof either single wires or twisted pair or coaxial cable. Further, it isan advantage of the present invention that rework of a printed circuitboard may be accomplished in a simple and inexpensive manner.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of a printed circuit board prior to arepair or rework.

FIG. 2 is a cross-section view of a plated-through hole of a printedcircuit board after a drill-out operation in accordance with the presentinvention.

FIG. 3A is a front cross-section view of a VR pin in accordance with afirst embodiment of the present invention.

FIG. 3B is a side cross-section view of a VR pin in accordance with afirst embodiment of the present invention.

FIG. 3C is a cross-section view of a VR pin inserted in a drilled-outhold in a printed circuit board according to a first embodiment of thepresent invention.

FIG. 3D is a top view of a portion of a printed circuit board showing aconfiguration of the connection wire as it is formed to make securemechanical and electrical connection with a solder ball pad inaccordance with a first embodiment of the present invention.

FIG. 4 is a cross-section view of a printed circuit board with aninsulated wire inserted in the drilled-out plated-through hole inaccordance with a second embodiment of the present invention.

FIG. 5 is a top view of a printed circuit board showing theconfiguration of the connection wire as it is formed so as to havesecure electrical and mechanical contact with a solder ball pad inaccordance with a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to FIG. 1, a cross-section view of a printed circuit board(PCB) 10 will be described. Printed circuit board 10 includes a topprinted circuit layer 12 and multiple internal printed circuit layers13, 14, 15, 16, 17, and 18, as well as bottom printed circuit level 20.PCB 10 also includes a number of plated-through holes 22, 24, and 26which permit connections between various levels of the multiple levelPCB 10. Integrated circuit chip 30 is mounted to a substrate 32 bysolder connections 34. The substrate 32 is mounted to the top printedcircuit level 12 of PCB 10 by solder ball grid array (BGA) 36.

Although FIG. 1 shows the so-called "dog bone design" of solder ballconnections (SBC) where the solder balls are offset from theplated-through holes in printed circuit board 10, an alternate designwould have the solder balls in BGA 36 axially aligned with the platedthrough holes 22, 24, 26 in printed circuit board 10. In such alternatedesign, the wire extending through the top of the PCB 10 must beshortened to avoid short circuiting to adjacent solder balls or pads.

For simplicity, the present invention will be described with respect tothe embodiment employing the dog bone design where the solder ballconnections are offset from the plated-through holes in the printedcircuit board 10.

Referring now to FIG. 2, the process according to the present inventionwill be further described. When repair or rework of a printed circuitboard 10 is required, a plated-through hole such as hole 22 is drilledout to remove the conductive material which plates the walls of hole 22.This leaves a hole without connections between various levels of themultiple level circuit board 10.

To achieve the desired repair or rework, a wire 60 or pin 40 within aninsulating sleeve 62, 48 (see FIGS. 3A, 3B, 3C, and 4) is inserted inthe drilled-out hole 22 in PCB 10 such that desired connections can bemade between ball grid array 36 on a top surface of PCB 10 and otherwires, whether single wire or coaxial cable to be connected to the postof a VR pin 40 (see FIG. 3A), or to a tail of wire 60 (see FIG. 4).

Referring now to FIGS. 3A, 3B, and 3C, a first embodiment of the presentinvention will be described.

A via replacement (VR) pin 40 is shown in FIG. 3A in a front sectionview, in FIG. 3B in a side section view, and in FIG. 3C inserted inmulti-level printed circuit board 10 in drilled-out hole (via) 22 andsecured by a fluid tight, mechanically strong material, such as epoxy.VR pin 40 has a lower post portion 42 which extends below the bottom ofPCB 10, a tail portion 44 which extends from the post portion 42 upwardthrough the via 22, and a Z-stop 46 which controls the verticalpositioning of the VR pin 40 within the via hole 22. A wire 46 isattached to tail portion 44 by a suitable electrically conductiveattachment mechanism such as welding. Wire 46 may typically be a smalldiameter (approximately three mils) gold plated wire. Wire 46 is ofsufficient length to extend out of hole 22 (FIG. 3C) and be bent overand affixed to ball grid array 36. An insulating sleeve 48 is placedover the wire 46 and tail 44 of VR pin 40. The insulating sleeve 48prevents contact between any of the intermediate printed circuit planes13, 14, 15, 16, 17, and 18 of PCB 10. Post 42 is the rigid extension ofVR pin 40 which provides sufficient strength and is of appropriatematerial or plating such that a connection wire (not shown) can beattached by soldering or other means of attachment.

Referring now to FIG. 3B, the side section view of VR pin 40 will bedescribed. Wire 46 is welded to tail 44 of VR pin 40 as described above.An epoxy araldite material 50 provides mechanical security betweensleeve 48, tail 44, and wire 46 and provides a liquid tight seal aroundwire 46 and tail 44.

Wire 46, which extends out of the top of hole 22, may be bent and formedto be in electrical and mechanical contact with dog bone 52 on which asolder bail of solder ball grid array 36 is attached. (See FIG. 3D.)

Referring now to FIG. 4, an alternate embodiment of the presentinvention will be described. Although FIG. 4 shows a coaxial cablehaving a wire 60 surrounded by an insulator 62 with a ground lead 66,wire 60 could also be a single conductor surrounded by an insulator 62and not a portion of a coaxial cable.

Wire 60 embedded in insulating material 62 is passed through via hole 22in printed circuit board 10, and the wire is bent into an appropriateform to match the dog bone configuration (see FIG. 5) for receiving asolder bail of solder bail grid array 36. The wire and insulator is heldin place and sealed with adhesive 64 which may be an epoxy material. Theground lead 66 of the coaxial cable may be soldered to an appropriateground connection, and the bottom of hole 22 may be sealed with epoxymaterial as described above.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A method for reworking a printed circuit board,having a first solder ball grid array attached thereto, the printedcircuit board having ball grid array pads mounted on one surfacecorresponding to the solder ball grid array, the method comprising thesteps of:removing the first ball grid array from the printed circuitboard; removing conductive material from a hole in the printed circuitboard to sever electrical connections between its corresponding ballgrid array pad and internal circuits and circuits mounted on an oppositesurface of the printed circuit board; inserting an insulated electricalconductor into the hole; electrically connecting and mechanicallyattaching a change wire to a first end of the electrical connector;forming a second end of the electrical conductor to be in proximity tothe corresponding ball grid array pad; and attaching a second solderball grid array to the printed circuit board such that a secureelectrical connection is formed between the second end of the electricalconductor and the corresponding ball grid array pad during solderreflow, thereby creating a new circuit between the change wire and thecorresponding ball grid array pad.
 2. The method according to claim 1,wherein the hole in the printed circuit board is a plated through holeand the step of removing its conductive material comprises precisiondrilling of the plated through hole.
 3. The method according to claim 1,wherein the electrical conductor is a rigid pin having first and secondends corresponding to the first and second ends of the electricalconductor, the pin having a wire electrically connected and mechanicallyattached to the second end of the pin, and a post at the first end ofthe pin.
 4. The method according to claim 1, wherein the forming stepfurther comprises the step of shaping the second end of the electricalconductor to conform to the shape of the corresponding ball grid arraypad.
 5. The method according to claim 1, further comprising the step ofconnecting a shield conductor of a coaxial cable change wire to acorresponding ball grid array pad on the printed circuit board.
 6. Themethod according to claim 1, wherein the first ball grid array isre-attached as the second ball grid array.